The objective of this research is to examine the role of glycoprotein oligosaccharides as information-bearing macromolecules involved in inter-\and intracellular communication. High performance liquid chromatographic methods for fractionation and analysis of anionic and neutral oligosaccharides and glycopeptides have been developed and utilized to establish the structures of the oligosaccharides present on human beta-glucuronidase and IgD. These studies have provided the means for preparation of well-characterized oligosaccharide probes to examine receptor specificity. Examination of the Man-6-PO[unreadable]4[unreadable]-specific receptor of fibroblasts, the Gal/GalNAc-specific receptor of hepatocytes, and the Man/GlcNAc-specific receptor of reticuloendothelial cells has demonstrated that each recognizes individual oligosaccharides in a highly specific manner. Utilizing glycoprotein and glycopeptide ligands, conditions have been established for uncoupling receptor-mediated uptake by the Gal/GalNAc-specific receptor from delivery of ligand to lysosomes, demonstrating that receptor recycling occurs from an intracellular vesicle with the same density as plasma membranes. Evidence has also been obtained with ionophores that is consistent with transmembrane regulation of the carbohydrate binding site of the receptor. Further studies of receptor regulation and characterization of the intracellular vesicle where ligand accumulates following uncoupling of delivery to lysosomes are in progress. A soluble lectin with Man/GlcNAc specificity has been isolated and characterized as well. This lectin is synthesized and secreted by rat hepatocytes and a rat hepatoma line in culture. Unusual properties include an as yet undefined post-translational modification at 15 to 30 min, assembly of subunits (Mr = 28,000) into a large molecular weight complex (approximately 600,000) prior to secretion, and slow rate of secretion (approximately 12 hrs for complete secretion). These unusual properties are under examination in an attempt to understand the function of this lectin. This soluble lectin displays specificity for the core portion of oligosaccharides. This lectin is clearly distinct from the Man/GlcNAcspecific receptor of reticuloendothelial cells. (A)